Just days away from unveiling some of the most innovative design changes in The Sunday Times' 186-year history, editor John Witherow and his lieutenants, led by ex-Independent on Sunday editor Tristan Davies, are still tweaking fonts, mastheads and layouts.

Yet, the atmosphere is stress-free - Witherow is oozing the sort of easy-going self-assuredness that comes from having spent 13 years in the editor's chair, making him the longest serving of all Rupert Murdoch's editors. The previous day, he'd even taken time out to go to Wimbledon, staying until 10.30pm, in the gloom, to witness Andy Murray's amazing five-set turnaround against Richard Gasquet.

The redesign exploits the new opportunity to have colour on every page, resulting from News International's £650m investment in colour presses, and comes with a bespoke news typeface, "Sunday Times Modern", new headline fonts, colour-coding of sections and spreads, a new masthead and, generally, "a more modern, fresher and livelier look".

By now you will have seen the results, unveiled on Sunday (6 July). When sister paper The Times unveiled a redesign a few weeks ago, it was hard to see a big difference, aside from the move of the leader to page two. But it's unlikely that anyone will say the same about The Sunday Times' revamp. When the paper employs colour on every broadsheet-sized page, in big bold sweeps, the result is dramatic.

Witherow reveals that Culture and the Sunday Times Magazine will be redesigned later in the year, but says he is not intent on revolution and that the paper's content and its placing will remain largely the same, albeit with more space for comment, with opportunities for reader interaction linked to the paper's website. Think Tank will explore and debate big ideas, while Little Britain in Atticus will give the paper's British eccentrics a "quirky" voice.

Critics say a dramatic overhaul is long overdue. Writing in The Guardian last year, former Sindy editor Peter Wilby described The Sunday Times as "unlovable and unexciting, exuding the dull, slightly irritable conservatism of a suburban golf club".

Declining salesWhether through dullness or price sensitivity, sales of the paper have been falling for the past two years, since the introduction of a £2 cover price.

Of course, The Sunday Times is not alone in suffering declining circulation, and Witherow points out that a paper still selling 1.2 million copies a week - it outsells its nearest rival by almost 2:1 - at two quid a go must be doing something right.

He is bullish about the future of Sunday papers, believing that "logically" their future is brighter than dailies. This future lies in an increasingly analytical approach to reporting news that has broken earlier in the week, probably online. Witherow claims that half The Sunday Times readers don't even read a daily paper, so there is a thirst for an in-depth read on Sundays.

He summarises the role of Sunday papers as "looking back, looking forward and analysis" and, interestingly, compares their fortunes with those of weekly news magazines.

He says: "The Economist continues to expand. With the welter of information hitting people, there's a demand to sit back at some stage and make sense of it - a Sunday paper can put the news into context."

Witherow even believes he can increase sales and attributes recent declines across the Sunday market to aggressive price increases. "Throughout the '90s and into the noughties, our circulation grew and I think we can do that again, as long as we can keep our price stable. There is still demand for a paper that provides good journalism and decent pictures, and £2 for a package like The Sunday Times is good value."

The package, at nine newsprint sections and three supplements, may be good value for those with the time to do it justice. But has it become too over-facing to many who have now given up on Sunday paper reading altogether, rather than suffer the guilt of tipping unread sections into the bin? Isn't a slimmed-down Sunday paper what readers, who now have so much leisure choice on Sundays, really want?

Great choice"Yes, some will find us too much, and that was always the argument against expanding and going multi-section, but the strategy has worked," he points out. "People like having sections." He adds that a new ad campaign, starring Peter O'Toole, is designed to push the idea that The Sunday Times provides great choice, but that you don't have to read every section. "And 80% of our newsprint is recycled," he laughs.

Witherow, 56, has been linked to a move upstairs into management and, with the revamp of the paper complete, might this be time for a new challenge? "Nah, I'm a journalist," he insists, "and doing these changes has been reinvigorating."

He also professes not to be nervous about the current efficiency drives being visited on his paper's commercial operations, instigated by Boston Consulting Group, being carried over to editorial.

"If they can suggest ways of producing the paper more efficiently so that we can transfer the savings into journalism, then that would be welcome, but cutting the editorial budget wouldn't," he says. "And James Murdoch understands that the quality of journalism is what matters."

Born: In South Africa, near JohannesburgFamily: Married to employment lawyer Sarah Linton, with three childrenHobbies: Tennis - he is a "fanatically enthusiastic, but bad tennis player" - and sailing. He owns a 40-year-old Salcombe Yawl, which he sails with Sir Keith Mills, who is masterminding a British assault on the America's Cup yachting race

WITHEROW on...Media sections I occasionally get asked to do one, but I think they're just the media writing for itself. Our Business section readers are people to whom the media is of mild interest, but it ain't worth two pages. If there's a good media story, we'll do it on merit.

Promotions They should reflect what we do, whether written word or photography. We did a Scrabble game that really fits with the paper because it's about words. But music and movie giveaways merely attract a reader for one issue and we need to move away from that. Getting readers to read the paper more often, from twice a month to every week, is a big opportunity for sales growth, and we will be offering a solus Sunday Times subscription to encourage this.

Journalism standards PRs are getting more powerful - there's more resource going into PR than journalism, so that has to be a worry. But it's up to journalists to cut through that. This is a golden age for journalists, with bigger, more global audiences for their work than ever before.